PI3 kinases are a family of lipid kinases that have been found to play a key role in the regulation of many cellular processes including proliferation, survival, carbohydrate metabolism, and motility. PI3Ks are considered to have an important role in intracellular signal transduction. In particular, the PI3Ks generate and convey signals that have important roles in cancer. PI3Ks are ubiquitously expressed, are activated by a high proportion of cell surface receptors, especially those linked to tyrosine kinases, and influence a variety of cellular functions and events. Although some PI3K activity is likely to be essential for cellular health, PI3Ks are a diverse group of enzymes for which there is increasing evidence of functional specialization. This opens up the possibility of developing isoform-selective inhibitors that can be used to treat cancer.
The primary enzymatic activity of PI3K is the phosphorylation of inositol lipids (phosphoinositides) on the 3-position of the inositol headgroup. PI3 kinases catalyze the addition of phosphate to the 3′-OH position of the inositol ring of inositol lipids generating phosphatidyl inositol monophosphate, phosphatidyl inositol diphosphate and phosphatidyl inositol triphosphate.
There are a total of eight mammalian PI3Ks, which have been divided into three main classes on the basis of sequence homology, in vitro substrate preference, and method of activation and regulation. Enzymes of a first class (Class I) have a broad substrate specificity and phosphorylate phosphatidylinositiol (PtdIns), PtdIns(4)P and PtdIns(4,5)P2. Class I PI3 kinases include mammalian p110α, p110β, p110δ and p110γ. Different members of the PI3-kinase family generate different lipid products. To date, four 3-phosphorylated inositol lipids have been identified in vivo. These lipids are bound by proteins that contain the appropriate lipid recognition module and which either act as effectors or transmit the PI3K signal onwards. The most familiar form of PI3K is a heterodimeric complex, consisting of a 110 kDa catalytic subunit now known as p110α and an 85 kDa regulatory/adapter subunit, p85α.
Phosphatidylinositol 3-kinase-alpha (PI3Kα), a dual specificity lipid and protein kinase, is composed of an 85 kDa regulatory subunit and a 110 kDa catalytic subunit. The protein includes a catalytic subunit, which uses ATP to phosphorylate PtdIns, PtdIns(4)P and PtdIns(4,5)P2. PTEN, a tumor suppressor, can dephosphorylate phosphatidylinositol (3,4,5)-trisphosphate (PIP3), the major product of PI3 kinase Class I. PIP3, in turn, is required for translocation of protein kinase B (AKT1, PKB) to the cell membrane, where it is phosphorylated and activated by upstream kinases. The effect of PTEN on cell death is mediated through the PI3Kα/AKT1 pathway.
PI3Kα has been implicated in the control of cytoskeletal reorganization, apoptosis, vesicular trafficking and proliferation and differentiation processes. Increased copy number and expression of the p110α gene (PIK3CA) is associated with a number of cancers such as ovarian cancer, cervical cancer, breast cancer, colon cancer, rectal cancer, endometrial cancer, stomach cancer, liver cancer, lung cancer, thyroid cancer, acute myelogenous leukemia (AML), chronic myelogenous leukemia (CML), and glioblastomas. In view of the important role of PI3Kα in biological processes and disease states, inhibitors of this protein kinase are desirable. The present invention provides PI3K inhibitors, particularly PI3Kα inhibitors, which are useful for treating PI3Kα-mediated diseases and conditions.
Mammalian target of rapamycin (mTOR) is a serine/threonine kinase of approximately 289 kDa in size and a member of the evolutionary conserved eukaryotic TOR kinases. The mTOR protein is a member of the PI3 kinase like kinase (PIKK) family of proteins due to its C-terminal homology (catalytic domain) with PI3 kinase and the other family members, e.g. DNA dependent protein kinase (DNA-PKcs), Ataxia-telangiectasia mutated (ATM).
It has been demonstrated that mTOR kinase is a central regulator of cell growth and survival by mediating multiple important cellular functions including translation, cell cycle regulation, cytoskeleton reorganization, apoptosis and autophagy. mTOR resides in two biochemically and functionally distinct complexes that are conserved from yeast to human. The rapamycin sensitive mTOR-Raptor complex (mTORC1) regulates translation by activation of p70S6 kinase and inhibition of eIF4E binding protein 4EBP1 through phosphorylation, which is the best-described physiological function of mTOR signaling. mTORC1 activity is regulated by extracellular signals (growth factors and hormones) through the PI3K/AKT pathway, and by nutrient availability, intracellular energy status and oxygen through the regulators like LKB1 and AMPK. Rapamycin and its analogues inhibit mTORC1 activity by disrupting the interaction between mTOR and raptor. The rapamycin-insensitive complex, mTORC2, was discovered only recently. Unlike mTORC1 which contains raptor, the mTORC2 complex contains other proteins including Rictor and mSin1. mTORC2 phosphorylates AKT at the hydrophobic Ser473 site, and appears to be essential for AKT activity. Other substrates of mTORC2 include PKCα and SGK1. How mTORC2 activity is regulated is not well understood.
The mTORC1 pathway can be activated by elevated PI3K/AKT signaling or mutations in the tumor suppressor genes PTEN or TSC2, providing cells with a growth advantage by promoting protein synthesis. Cancer cells treated with the mTORC1 inhibitor rapamycin show growth inhibition and, in some cases, apoptosis. Three rapamycin analogues, CCI-779 (Wyeth), RAD001 (Novartis) and AP23573 (Ariad) are in clinical trials for the treatment of cancer. However response rates vary among cancer types from a low of less than 10% in patients with glioblastoma and breast cancer to a high of around 40% in patients with mantle cell lymphoma. Recent studies demonstrated that rapamycin can actually induce a strong AKT phosphorylation in tumors by attenuating the feedback inhibition on receptor tyrosine kinases mediated by p70S6K, one of the downstream effectors of mTORC1. For example, in Phase I clinical trials of RAD001, an increase in pAKT (+22.2 to 63.1% of initial values) was observed after dosing. If mTORC1 inhibition-induced phospho-AKT leads to increased cancer cell survival and acquisition of additional lesions, this could counteract the effects of growth inhibition by rapamycin analogues and explain the variable response rate. Therefore, identifying and developing small molecules that target the catalytic activity of mTOR (inhibiting both mTORC1 and mTORC2) will lead to more effective therapeutics to treat cancer patients by preventing the activation of AKT that is caused by mTORC1 specific inhibitors like rapamycin and its analogues. Dysregulated mTOR activity has been shown to associate with variety of human cancers such as breast, lung, kidney, brain, ovarian, colon, cervical, endometrial, prostate, liver, thyroid, GI tract, blood and lymphoma and other diseases such as hamartoma syndromes, rheumatoid arthritis, multiple sclerosis. In view of the important role of mTOR in biological processes and disease states, catalytic inhibitors of this protein kinase are desirable. The present invention provides kinase inhibitors, specifically PIK kinase inhibitors, more specifically, mTOR inhibitors, which are useful for treating diseases mediated by kinases, specifically PIK kinases, more specifically, mTOR.